Coccidiosis and the Poultry Industry

By H. David Chapman, Center of Excellence for Poultry Science at the University of Arkansas's Avian Advice - Coccidiosis is a parasite infection of chickens that in the past caused catastrophic losses to the developing poultry industry in the United States. Today, thanks to the discovery of many effective drugs, the disease is well controlled. Indeed, it is doubtful if the industry could have reached its present size without effective means to control coccidiosis.

20 March 2006

6 minute read

Coccidiosis and the Poultry Industry - By H. David Chapman, Center of Excellence for Poultry Science at the University of Arkansas's Avian Advice - Coccidiosis is a parasite infection of chickens that in the past caused catastrophic losses to the developing poultry industry in the United States. Today, thanks to the discovery of many effective drugs, the disease is well controlled. Indeed, it is doubtful if the industry could have reached its present size without effective means to control coccidiosis.

Coccidiosis

We should be on our guard however, because the causative organism (a microscopic parasite with the scientific name Eimeria) is still present in most poultry flocks. Eradication has proved impossible. Therefore we should be aware of the conditions that make coccidiosis a threat to the health of our birds.

The Life Cycle

The parasite completes its life cycle in the intestine of the bird, multiplying in the cells that digest and absorb nutrients and eventually destroying them. Two of the commonest species (Eimeria acervulina and Eimeria maxima) develop in the mucosa of the anterior and mid intestine and the malabsorption that accompanies destruction of host cells results in poor growth and impaired feed conversion. Another common and widely known species is Eimeria tenella that develops in the paired cecal pouches where it damages the entire mucosa; this results in hemorrhage (with blood in the droppings) and, in severe cases, death of the bird. Eimeria necatrix also causes hemorrhage but, in the small intestine rather than the ceca. It is most frequently found in older birds reared for egg production.

Transmission

The transmission stage of the parasite is a microscopic egg shaped cyst (known as the oocyst). Oocysts are shed in the droppings and undergo a process known as sporulation that takes 24-48 hours; after this the oocyst is infective if ingested by a bird. An important aspect of the life cycle of these parasites is that the severity of the disease is proportional to the number of sporulated oocysts ingested. Thus, management of the disease requires the adoption of sanitary and hygienic procedures to reduce the level of exposure to infection. Sporulation is favored by moisture. Therefore it is important to maintain dry litter, especially around drinkers and feeding areas. Maintaining dry litter will reduce oocyst numbers and the likelihood that birds will be exposed to parasite numbers that will cause clinical coccidiosis.

Control

A chicken is shown above exhibiting symptoms of coccidiosis, a parasite infection that in the past has caused catastrophic losses to the industry.

Control of coccidiosis has been achieved by the use of drugs that kill the parasite before it can develop in the chicken. In the 1950’s and occasionally today, drugs were often included in the drinking water to treat sick birds. Unfortunately the onset of coccidiosis is rapid and the signs of disease (such as huddling, ruffled feathers, off feed) are seen with many other poultry diseases. Treatment often came too late to prevent serious production losses. A preventative approach is therefore desirable and this is achieved by incorporation of drugs in the starter and grower feeds. The most widely used drugs are known as ionophores. These compounds inhibit the development of the parasite but, do not prevent the acquisition of natural immunity by the bird so that they can be withdrawn from the feed well before the birds are sold. The poultry industry has devised many programs using drugs for the control of coccidiosis. Yet coccidosis organisms can quickly become resistant to drugs. Thus, in the spring and early summer “shuttle” programs are often employed in which a synthetic drug (so called “chemicals”) is incorporated in the starter feed and an ionophore in the grower. Rotation programs in which different drugs are used in successive flocks have also been widely adopted.

Vaccines

An entirely different approach to the control of coccidiosis involves the use of vaccines. Vaccines in which birds are administered small numbers of sporulated oocysts have long been available in the USA. In the past vaccines have principally been employed during the rearing phase of egg-laying birds. The introduction of novel methods of administration (such as with a spray-cabinet in the hatchery) has made vaccination of broilers more feasible. Researchers are actively seeking better means to safely immunize birds against coccidiosis and although there are many technical hurdles to overcome, progress is being made and new vaccines seem likely in the future.

Problems

As is often the case, success in controlling a disease is often accompanied by a downside. In the case of the coccidiosis parasite Eimeria has proved to be very adaptable, eventually acquiring resistance to the widely used drugs. It has therefore been necessary to constantly discover new compounds to replace those that are no longer effective. Unfortunately, this process is now vastly expensive and many companies have been discouraged from pursuing new drug discovery. Vaccines are seen as a likely alternative but, the decreased funding available for basic research into, for example, mechanisms of immunity may prevent progress in the future.

Management

As long as chickens are raised on the ground and therefore in contact with their feces, then coccidiosis will remain a threat to the poultry industry. Good management however, plus the adoption of effective control programs, whether by chemotherapy or vaccination, can serve to reduce the risk. In 1991, following the first ever flock of broilers raised at the University of Arkansas Applied Broiler Research Farm at Savoy, we identified three species of Eimeria present in the litter. These species are still present today after many flocks have been successfully raised on the site. By a combination of good management and adoption of control programs recommended by the integrator, coccidiosis has not so far been a problem. It is hoped that this situation will continue in the future.